Investigations will be continued of the properties of idiotype-specific suppressor T cells and of soluble substances which may be elaborated from such suppressor cells. Efforts will be made to isolate suppressor factors either by sonication or by repeated freezing and thawing of the cells. Such factors will be adoptively transferred into mildly irradiated recipients which will subsequently be immunized against the phenylarsonate group to determine whether or not the characteristic idiotype appears. A systematic study will be continued of the factors responsible for the production of large numbers of idiotype-specific suppressor T cells, as identified by rosette formation. Parameters to be investigated include the completeness of the suppressed state, the role of antigen in inducing suppressor T cells and the mode of presentation of antigen, either as a soluble protein or as protein attached to syngeneic lymph node cells. Investigations will be continued to determine the nature of the idiotypic determinants present on soluble suppressor factors isolated from T cells, which are capable of adoptively transferring idiotype-specific suppression of delayed hypersensitivity. The idiotype to be used in these investigations is that associated with antiphenylarsonate antibodies of A/J mice.